Generally, a torque converter transmits engine torque to a transmission through fluid, and such fluid usually causes torque transmitting loss due to fluid friction. To avoid such fluid friction loss, a lock-up clutch provided at the torque converter is engaged for transmitting engine torque when a rotation speed of a pump impeller provided at the input side becomes similar to a rotation speed of a turbine runner provided at the output.
Recently, a locked up condition of the clutch has been expanded for improving fuel consumption. Corresponding to such trend, the torque converter also includes an engaging hydraulic pressure chamber (lock up chamber) between a front cover and a front cover hub for improving the lock up engaging accuracy and a durability of the torque converter, and the number of such torque converter having such chamber has been increased.
A known torque converter is disclosed in U.S. Pat. No. 5,533,602 and SAE 2002-01-0935, which includes a front cover hub processed by forging or grinding and an oil path formed by drilling the front cover hub for providing a hydraulic pressure to the engaging hydraulic pressure chamber. The front cover hub is fixed to a front cover by pressing or welding.
The cost of such torque converter having aforementioned configuration has been increased due to the forging or grinding process applied to the front cover hub.
Thus, a need exists for a torque converter to decrease the cost thereof without lessening the virtual function thereof.